The 27-year-old set a new Olympic record of 51.96s ahead of Hong Kong’s Siobhan Haughey, who timed 52.27s, and fellow Australian Cate Campbell (52.52s).

Only Swedish sprint star Sarah Sjostrom has ever gone faster, when she set the world record of 51.71s at the Budapest world championships in 2017.

She finished sixth today.

“Honestly I still can’t believe I just won a gold medal,” said an overwhelmed McKeon.

“I think it’ll probably take a while to sink in then the emotions will really come out. I knew that I’ve been working hard and I was the best prepared.”

It was McKeon’s fourth medal in Tokyo having already clinched gold and bronze in relays and came third in the 100m butterfly, matching her four-medal tally from Rio.

The 27-year-old had signalled her intent in the Wednesday heats, lowering the Olympic record, with her time in the final making her and Sjostrom the only swimmers ever to breach 52 seconds.

“I’ve never actually won at Olympics or worlds (gold) individually, so to see that one next to my name,” added McKeon.

“I didn’t even look at my time, I just went for the place because that’s what Olympics is about. It’s getting your hand on the wall and you want that gold medal.”

Haughey has been a revelation in Tokyo, with the silver medal going with the one she sensationally won behind Ariarne Titmus in the 200m final.

The title was vacant after American defending champion Simone Manuel failed to qualify for the Games at the US trials in a shock result.